The Effective Temperatures of O-type Stars from UV spectroscopy

We present an analysis of high resolution spectra in the far-UV -- UV range (~905-2000\AA) with non-LTE, spherical, hydrodynamical, line-blanketed models, of three O-type Galactic stars, and derive their photospheric and wind parameters. These data extend previously analyzed samples and fill a gap in spectral type coverage. The combined sample confirms a revised (downward) effective temperature scale with respect to canonical calibrations, as found in our previous works from UV and optical spectra, and in recent works by other authors.